1. Field of the Invention
The present invention relates to a document reading apparatus which irradiates light toward document and generates image data representing content described in the document through photoelectric conversion of the reflected light and a document reading method.
2. Description of the Related Art
Generally, a document reading apparatus is configured to, after a document is irradiated with light from light source, guide the reflected light from a document surface to an photoelectric conversion element. Typically, as a document for reading, a paper document with some irregularities, e.g., bumps and dents, thereon is used. However, a document with metallic gloss or photos etc., may be used as a document for reading. The term “metallic gloss” refers gold color or silver color having very high glossiness like the document on which foils are transferred through hot stamping. The photoelectric conversion element generates image data representing content printed on such a document.
FIGS. 8 and 9 are schematic diagrams illustrating, with arrow lines, directions to which lights irradiated toward general paper document are reflected. If a document surface of paper document 50 is rough and many fine irregularities exist thereon, radiation light 60 is respectively reflected by the irregularities, as shown in FIG. 8. Therefore, reflected light 71 is diffused in various directions. On the other hand, the reflected light 71 of the radiation light 60 irradiated toward the document surface of the document 51 having high glossiness is, as shown in FIG. 9, almost equal to a regular reflection light 72. The regular reflection refers reflection in a direction symmetric with respect to an incident angle, in which the incident angle θ is equal to the reflection angle θ. The document 51 having high glossiness includes a document on which foils are transferred through hot stamping, photos and the like.
As above, depending on a surface state of the document (state of the part of the document to be read, hereinafter referred to as “reading area”), the ratio of the regular reflection light 72 largely changes.
In a conventional document reading apparatus, however, lights diffusing in a vertical direction with respect to the surface of a document 50 and a document 51 are guided to photoelectric conversion element. Therefore, in case of the document 51 having high glossiness, though the ratio of the regular reflection light 72 with respect to the total reflected light 71 is very high, the regular reflection light 72 is not guided to the photoelectric conversion element. Unfortunately, as a result, the image data represents an image with low luminance.
A technology could be a solution to this problem is disclosed, for example, in Japanese Patent Application Laid-open No. 2004-274299 as an image reading apparatus. The image reading apparatus comprises a normal first light source for reading paper document. In addition to this, the image reading apparatus comprises a second light source dedicated to reading gloss document.
A document is irradiated with light by the second light source, which is the same emission wavelength as the first light source, at an irradiation angle different from that of the first light source. In case of the document having high glossiness, the regular reflection light of the second light source is guided to the photoelectric conversion element. Further, providing light adjustment means such as liquid crystal shutter between the second light source and the document reduces the irradiation amount toward the document surface by the second light source.
The image reading apparatus as disclosed in Japanese Patent Application Laid-open No. 2004-274299, however, still has following problems.
FIG. 10A is a schematic diagram illustrating reflected lights in reading areas A to F of a document 52 having a surface which is an ideal mirror in terms of its surface condition such as glossiness, flatness, surface roughness. FIG. 10B shows image data (which is a luminance value in 256 gradations) in reading areas A to F which are read and output by the image reading apparatus as disclosed in Japanese Patent Application Laid-Open No. 2004-274299. Further, FIG. 11A is a schematic diagram illustrating reflected light in the reading areas A to F in case of the document 51 having high surface glossiness. FIG. 11B shows image data (which is a luminance value in 256 gradations) in the reading areas A to F which are read and output by the image reading apparatus as disclosed in Japanese Patent Application Laid-open No. 2004-274299.
In the image reading apparatus as disclosed in Japanese Patent Application Laid-Open No. 2004-274299, a first mirror 91 is placed in a path of the regular reflection light of the second light source. Then, the regular reflection light reflected by the first mirror 91 is guided to the photoelectric conversion element 95 through a second mirror 92 and a third mirror 93. As shown in FIG. 10A, if the surface of the document is an ideal mirror surface which only reflects the regular reflection light, the reflected light travels toward path 100, which is directed to the first mirror. Therefore, as shown in FIG. 10B, correct image data are obtained in the reading areas A to F. It is general, however, that even the document having high glossiness, there are some irregularities on the surface. Therefore, most reflected lights turn to the regular reflection light, however, not all the reflected lights turn like that.
In this case, in the image reading apparatus as disclosed in Japanese Patent Application Laid-open No. 2004-274299, in which light is irradiated only from one direction, reflection light which travels in a direction different from that of the regular reflection light is generated as shown in FIG. 11A. This results in a generation of pixel which is almost incapable of guiding the reflected light to the photoelectric conversion element 95. This generates shadowed image data of read areas A and F, as shown FIG. 11B, for example. When such image data are read, there will be many black shadows (hereinafter referred to as irregular shadow) on metallic gloss.